Four Channel 7-Segment Display Module 
for multiplexing with arduino Easy to use

This listing is for a neat little four-channel common cathode 7-segment display module.  It requires 3.3-5v to operate.  You can multiplex signals to this module using the on board points that are labelled on the board.  I`ll go through an explanation of how the board works.   The use should connect 3.3-5v to the VCC line on the board.  This powers each of the displays.  There are four active-low control pins (D1, D2, D4, and D4).  These pins act to activate a segment via an active low signal (0v-GND).  By default, these lines are hight, which means that when power is applied, none of the segments are activated.  When you apply 0v-GND to say D1, then the first segment will be activated.  However, nothing will light up.  You now need worry about the segment lines.  If you are not educated as to how a 7-segment display works, you might want to learn before you buy this.  This is where the multiplexing comes into play.  Each of the four displays have the internal segment LEDs tied together.   The segment lines need a current limiting resistor applied, and can not be driven directly.  If you have the D1 segment activated, and the rest deactivated, and you connect ground to segment (A) through a 220R-600R resistor, then 5v will travel through the (A) segment on the D1 display through to ground.  The current is limited via the resistor.  If you have no resistor, then you will burn out that segment.  If you have all four of the displays activated (D1-D4 lines are all grounded), and you apply ground to segment (C) through a current limiting resistor, then all of the (C) segments on all four of the displays will light up.

You must use a microcontroller to multiplex commands to turn displays on and off, and to send segment data.  If you`re not understanding the above explanation, or don`t understand how multiplexing works, then you`re not going to find much use for this little gadget.  Each of the displays have an on board transistor and a resistor at the base of each of the transistors to protect it.  All you need to to is add 220R-600R resistors in series between your signal lines and the segment lines (A-H).  The D1-D4 lines do not need resistors.  If you have any questions, please do not hesitate to ask!